It is well known for lubricating oils to contain a number of surface active additives (including antiwear agents, dispersants, or detergents) used to protect internal combustion engines from wear, soot deposits and acid build up. Often, such surface active additives including zinc dialkyldithiophosphates (common antiwear additive for engine lubricating oils is zinc dialkyldithiophosphate (ZDDP)) or dispersants can have harmful effects on bearing corrosion or friction performance.
Many of these additive chemistries are corrosive to lead or copper. It is difficult for formulators to meet the present engine oil specifications by employing certain beneficial additives while also meeting the specification for lead or copper corrosion. With the introduction of industry specifications and legislation to reduce emissions, there are tighter limits on ash-containing, sulfur-containing and phosphorus-containing components. For example, industry specifications such as API CJ-4, as well as MACK T-11 and Mack T-12 tests, have been introduced for heavy duty diesel engines.
There has been a commercial trend for reduction in emissions (typically reduction of NOx formation, SOx formation) and a reduction in sulfated ash in engine oil lubricants. Consequently, the amounts of phosphorus-containing antiwear agents such as ZDDP, overbased detergents such as calcium or magnesium sulfonates and phenates have been reduced. As a consequence, ashless additives have been contemplated to provide friction or antiwear performance. It is known that surface active ashless compounds such as ashless dispersants may in some instances increase corrosion of metal, namely, copper or lead. Copper and lead corrosion may be from bearings and other metal engine components derived from alloys using copper or lead. Consequently, there is a need to reduce the amount of corrosion caused by ashless additives.